ok got a 88 reg cab 4x4 v-6 5spd.....had a pretty bad vibration when i bought the truck....put new u-joints in thinking this would solve the problem, but did not....done alignment, balance, ect.....no change...tonight after reading in here i took the rear driveshaft out locked it four wheel drive and took off.....and lo and behold no vibration....so i know it's something in the driveshaft but don't know what...the shaft is splined and i can get a very small amount of movement there but???? does anyone know the proper alignment of the front to rear u-joints, the ones i took out seemed fairly new and i just marked where everything was and put it back. or what else can i do? thanks

 

That is called phasing, see below for the answer to your question:
- http://www.4crawler.com/4x4/CheapTri....shtml#Phasing

 

thanks for the link....i do have it aligned properly....so i must have some other issue. guess i'll check some local junk yards and see if i can locate one.